Connection between two shaft ends, positioned coaxially one behind the other, of a gas shuttle valve in an internal combustion engine and a valve actuator

ABSTRACT

A connection between two shaft ends situated coaxially one behind the other, of a gas exchange valve of an internal combustion engine and a piston rod of a valve actuator is provided, where at least one coupling member at least partially surrounds the shaft ends. The coupling member is radially compressed with respect to the two shaft ends by at least one compressing member to produce static friction locking between each shaft end and the coupling member that transfers the actuating motion of valve actuator to gas exchange valve in a slip-free manner. As a result, the fatigue strength of the connection may be increased and its assembly and disassembly may be simplified.

FIELD OF THE INVENTION

The present invention relates to a connection between two shaft endssituated coaxially one behind the other of a gas exchange valve of aninternal combustion engine and of a valve actuator, where at least onecoupling member at least partially surrounds the shaft ends.

BACKGROUND INFORMATION

A connection is known from published patent document EP 0 279 265 B1,where the coupling member includes two half-shells whose radiallyexternal peripheral surfaces are cylindrical, and whose radiallyinternal peripheral surfaces are conical in a manner complimentary tothe piston rod ends of the valve actuator, which are tapered conicallywith respect to one another, and to a shaft of the gas exchange valve.To prevent the two half-shells from falling apart, a cylindricalcoupling sleeve is held to the half-shells by the axial prestress forceof a valve spring which is supported on the bottom of the screw sleeveand is pushed over them, and the shaft of the gas exchange valve extendsthrough an opening in the bottom of the screw sleeve. The two shaftends, which are tapered relative to each other, have at the extremityflanges that are widened in a plate-like manner and grip the couplingmember formed by the half-shells from behind, so that the two shaft endsare connected to one another by the coupling member in a form-lockingmanner. At the form-locking junction between the conical runout of theshaft ends and the extreme flanges, the cross-section is weakened ineach case by a distinct groove, which has a negative effect on thefatigue strength of the connection. This represents a significantdisadvantage especially with regard to the high number of load changesthat gas exchange valves of internal combustion engines are subjectedto.

SUMMARY OF THE INVENTION

Due to the frictionally engaged connection between the coupling memberand the shaft ends, no undercuts are necessary such as groove-likeindentations which weaken the cross-section of the shaft ends and/or ofthe coupling member. Consequently, the connection of the presentinvention is distinguished by a high degree of fatigue strength.

According to an exemplary embodiment, the prestress applied to thecoupling member by the compressing member may be adjustable. For thispurpose, the compressing member includes at least two conicalcompressing sleeves which may be axially screwed against one another andhave conical surfaces that may be wedged against conical compressingsurfaces formed on the radially external peripheral surface of thecoupling member. A defined radial prestress may be generated between thecoupling member and the shaft ends as a function of the degree oftightening of the conical compressing sleeves. This may be advantageouswith regard to the surface conditions that may differ depending on thegas exchange valve or the valve actuator and to the correspondinglydifferent friction coefficient in that the radial prestress necessaryfor slip-free static friction locking may be adjusted.

Viewed in the circumferential direction, the coupling member has amulti-part design and preferably includes at least two half pipe-shapedcoupling wedges, which complement one another to form a sleeve. Eachcoupling wedge has on its outer peripheral surface two compressingsurfaces situated radially one behind the another and expandingconically with respect to one another, and each compressing surface maybe assigned to one conical surface of one of the conical compressingsleeves. Both conical compressing sleeves may be expediently providedwith a contact surface for a screw tool.

According to a further embodiment, positioning projections andpositioning recesses that preferably intermesh with play may be providedon the coupling member and on each shaft end for positioning thecoupling member on the shaft ends. This ensures that the coupling membermay be compressed in a defined position with respect to the shaft ends,and may result in a balanced surface covering. On the other hand, theloose intermeshing of the positioning projections and recesses, reducesfatigue strength-lowering notch stresses. According to an exemplaryembodiment, the radially internal, cylindrical peripheral surface of thecoupling wedges has annular protuberances that extend in thecircumferential direction, and each annular protuberance may be assignedto an annular groove of a shaft end. The annular protuberances andannular grooves have an essentially semicircular cross section, theinner radius of the annular grooves being greater than the outer radiusof the annular protuberance in order to prevent direct material contactas much as possible, and to keep the notch stresses caused by theannular grooves as low as possible.

Finally, the connection between the valve actuator and the gas exchangevalve may be situated in an accessible region outside of a valveactuator housing. Therefore, in the event that repairs may be needed, itmay be very easy to replace a gas exchange valve or a valve actuator,and it may not be necessary to dismantle the valve actuator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a lateral view of a cross-section of a preferred specificembodiment of a connection of the invention between a shaft end of a gasexchange valve of an internal combustion engine, and a piston rod of avalve actuator.

FIG. 2 shows a view of a cross-section along line II—II from FIG. 1.

FIG. 3 shows an enlarged view of detail A from FIG. 1.

DETAILED DESCRIPTION

Only a gas exchange valve 1 of a valve mechanism of an internalcombustion engine is shown in FIG. 1. The gas exchange valve 1 isactuated by a piston rod 2 of a valve actuator 4 such that it performsupward and downward opening and closing movements. For this purpose,piston rod 2 of valve actuator 4 and a shaft 6 of gas exchange valve 1may be situated coaxially one behind the other, and a shaft end 8 ofpiston rod 2, and a shaft end 10 of shaft 6 of gas exchange valve 1, maybe situated opposite one another. Piston rod 2 and shaft 6 of gasexchange valve 1 preferably have the same diameter. To be able totransfer the pressing motion and/or pulling motion of piston rod 2 togas exchange valve 1, a coupling member 14 is provided that at leastpartially surrounds shaft end 8 of piston rod 2 as well as shaft end 10of gas exchange valve 1. Viewed in the circumferential direction,coupling body 14 preferably has a multi-part design and includes twohalf pipe-shaped coupling wedges 16, 18, which complement one another toessentially form a sleeve, as is best seen in the sectional view in FIG.2. The radially internal peripheral surfaces of both coupling wedges 16,18 may be cylindrical and may have the same radius as piston rod 2 andshaft 6 of gas exchange valve 1. Viewed in the circumferentialdirection, both coupling wedges 16, 18 do not connect to one anotherwithout gap, but a narrow opening 20 remains at both joints, so thatthere may be a circumferential compensation for both coupling wedges 16,18 when a radial pressure may be exerted on them from the outside.

As can best be seen in FIG. 1, intermeshing positioning projections andpositioning recesses may be provided on coupling member 14 and on eachshaft end 8, 10 for positioning coupling member 14 on shaft ends 8, 10.This ensures that coupling member 14 may be situated in a definedposition with respect to both shaft ends 8, 10 and that results in abalanced surface covering. According to the preferred specificembodiment, each radially internal, cylindrical peripheral surface ofboth coupling wedges 14, 16 has two annular protuberances extending inthe circumferential direction, a top annular protuberance 22 engagingwith a circumferential annular groove 24 formed on shaft end 8 of pistonrod 2, and a bottom annular protuberance 26 engaging with an annulargroove 28 in a shaft end 10 of gas exchange valve 1. Annularprotuberances 22, 26 and annular grooves 24, 28, which may be assignedto one another, have an essentially semicircular cross section as can beseen, particularly, in enlarged view A in FIG. 3. Annular protuberances22, 26 do not abut against annular grooves 24, 28 of the shaft endssince their inner radius is greater than the outer radius of annularprotuberances 22, 26.

Both half pipe-shaped coupling wedges 16, 18 have on their radiallyexternal peripheral surface compressing surfaces 30, 32 disposed onebehind the other and expanding conically toward one another in order tobe able to compress couple wedges 16, 18 radially with respect to bothshaft ends 8, 10. For this purpose, a compressing member, preferably twoconical compressing sleeves 34, 36, which may be axially screwed againsteach other and have conical surfaces 38, 40, may be provided that may bewedged against compressing surfaces 30, 32 of coupling wedge 16, 18. Adefined radial prestress may be produced between coupling wedges 16, 18and both shaft ends 8, 10 as a function of the screwing degree of thetwo conical compressing sleeves 34, 36. Since the motion of piston rod 2of valve actuator 4 may be transferred to gas exchange valve 1 in aslip-free manner, the prestress must be so great that there may alwaysbe static friction between coupling wedges 16, 18 and shaft ends 8, 10under the forces acting during operation. Of the two compressingsurfaces 30, 32 of a coupling wedge 16, 18, a top compressing surface 30may be assigned in each case to a conical surface 38 of top conicalcompressing sleeve 34, and a bottom compressing surface 32 may beassigned in each case to a conical surface 40 of bottom conicalcompressing sleeve 36. Top conical compressing sleeve 34 may be screwedinto bottom conical compressing sleeve 36 because radially externalperipheral surface of top conical compressing sleeve 34 may be providedwith an external thread 42, and the radially internal peripheral surfaceof bottom conical compressing sleeve 36 may be provided with an internalthread 44 having the same diameter. Both conical compressing sleeves 34,36 may be provided at their ends facing away from one another with acontact surface 48, 50 for a screw tool. Threads 42, 44 may beconsequently outside of the force flux that arises when the valve may beactuated and extends from piston rod 2 over the two coupling wedges 16,18 to shaft 6 of gas exchange valve 1 and may only be subjected to thestatic prestress for procuring the friction locking between couplingwedges 16, 18 and shaft ends 8, 10. Since annular protuberances 22, 26of both coupling wedges 16, 18 do not rest against annular grooves 24,28 of shaft ends 8, 10, the form locking portion generated by couplingwedges 16, 18 being radially pressed outweighs the form locking portioncaused by the mutually assigned annular protuberance/annular groovepairings in the case of the coupling of piston rod 2 and shaft 6 of gasexchange valve 1. Consequently, the annular protuberance/annular groovepairings may be foremost used to fix the coupling member 14 to shaftends 8, 10 and may, therefore, have small dimensions. Consequently,their stress concentration at shaft ends 8, 10 and their influence onthe fatigue strength of the connection may be minimal.

As seen in FIG. 1, the described connection between piston rod 2 ofvalve actuator 4 and shaft 6 of the gas exchange valve may be situatedoutside of a valve actuator housing 52 of valve actuator 4 in an easilyaccessible region, so that valve actuator 4 and gas exchange valve 1 maybe both easy to assemble and disassemble as individual modules.

According to a further specific embodiment, coupling member 14 may alsobe designed as a one-piece sleeve instead of as a two-piece sleeve,where a continuous slit extends in the axial direction and needs to beprovided, in this case, in the wall of the sleeve, in order to enablecompensating motion of the one-piece sleeve in the circumferentialdirection when radial prestress may be applied from the outside by thewedge effect of conical compressing sleeves 34, 36.

What is claimed is:
 1. A connection between two adjacent coaxial shaft ends of a gas exchange valve of an internal combustion engine and a piston rod of a valve actuator, comprising: at least one coupling member which at least partially surrounds the shaft end of the gas exchange valve and the shaft end of the piston rod; and at least one compressing member, wherein the coupling member is radially compressed with respect to the two shaft ends by the at least one compressing member to produce a static friction lock between each shaft end and the coupling member, whereby an actuating motion of the valve actuator to the gas exchange valve is transferred in a slip-free manner.
 2. The connection as recited in claim 1, wherein the compressing member comprises at least two conical compressing sleeves which are adapted to be axially screwed against one another, wherein the sleeves have conical surfaces which are adapted to be wedged against conical compressing surfaces formed on radially external peripheral surface of the coupling member, to generate a radial prestress which produces a static friction lock between the coupling member and the shaft ends.
 3. The connection as recited in claim 2, wherein the conical compressing sleeves have a contact surface for a screw tool.
 4. The connection as recited in claim 2, wherein the coupling member comprises at least two half pipe-shaped coupling wedges adapted to form a sleeve and each having on its radially external peripheral surface two compressing surfaces situated one behind the other and expanding conically toward one another, and wherein each compressing surface mates with a corresponding conical surface of one of the conical compressing sleeves.
 5. The connection as recited in claim 4, wherein the coupling wedges have on their radially internal, cylindrical peripheral surface at least two annular protuberances which extend in the circumferential direction, and wherein at least one annular protuberance is adapted to mate with a corresponding annular groove on a shaft end.
 6. The connection as recited in claim 5, wherein the annular protuberances and annular grooves have an essentially semicircular cross-section, and wherein the inner radius of the annular grooves is greater than the outer radius of the annular protuberances.
 7. The connection as recited in claim 1, wherein the connection is situated in an accessible region outside of a valve actuator housing.
 8. The connection as recited in claim 1, further comprising positioning projections and positioning recesses provided on the coupling member and each shaft end for positioning the coupling member with respect to the shaft ends. 